U.S. patent number 7,224,320 [Application Number 11/132,761] was granted by the patent office on 2007-05-29 for small wave-guide radiators for closely spaced feeds on multi-beam antennas.
This patent grant is currently assigned to ProBrand International, Inc.. Invention is credited to Scott J. Cook.
United States Patent |
7,224,320 |
Cook |
May 29, 2007 |
Small wave-guide radiators for closely spaced feeds on multi-beam
antennas
Abstract
A relatively low cost, easy to install and aesthetically
pleasing digital video broadcast from satellite (DVBS) elliptical
horn antenna designed to receive satellite television broadcast
signals with circular polarity. This type antenna may be
implemented as a multi-beam, multi-band antenna with closely spaced
antenna feed horns operable for simultaneously receiving signals
from multiple satellites that are closely spaced from the
perspective of the antenna.
Inventors: |
Cook; Scott J. (Woodstock,
GA) |
Assignee: |
ProBrand International, Inc.
(Marietta, GA)
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Family
ID: |
35456749 |
Appl.
No.: |
11/132,761 |
Filed: |
May 18, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050259025 A1 |
Nov 24, 2005 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60572080 |
May 18, 2004 |
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60571988 |
May 18, 2004 |
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Current U.S.
Class: |
343/772; 343/776;
343/786 |
Current CPC
Class: |
H01Q
13/0225 (20130101); H01Q 19/17 (20130101); H01Q
25/007 (20130101) |
Current International
Class: |
H01Q
13/00 (20060101) |
Field of
Search: |
;343/772,779,776 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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G 90 13 455.9 |
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Mar 1991 |
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DE |
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57157603 |
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Sep 1982 |
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JP |
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WO 01/67555 |
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Sep 2001 |
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WO |
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Other References
Eine Schussel fur funf Satelliten. FUNKSCHAU, Jun. 14, 1991,
Munich, Germany. cited by other.
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Primary Examiner: Dinh; Trinh Vo
Attorney, Agent or Firm: Mehrman; Michael J. Mehrman Law
Office PC
Parent Case Text
REFERENCE TO RELATED APPLICATIONS
This application claims priority to commonly-owned copending U.S.
Provisional Patent Application Ser. No. 60/572,080 entitled "Small
Wave-Guide Radiators For Closely Spaced Feeds on Multi-Beam
Antennas" filed May 18, 2004, which is incorporated herein by
reference; and U.S. Provisional Patent Application Ser. No.
60/571,988 entitled "Circular Polarization Technique for Elliptical
Horn Antennas" filed May 18, 2004, which is also incorporated
herein by reference.
Claims
The invention claimed is:
1. An antenna configured to simultaneously receive signals from
multiple satellites that are closely spaced from the perspective of
the antenna; comprising: at least three closely spaced antenna feed
horns arranged in a substantially linear array along a linear axis;
a substantially elliptical reflector defining a major axis for
feeding signals to the closely spaced antenna feed horns; a first
feed horn of the array having an exterior contour that defines a
first indentation; a second feed horn of the array having an
exterior contour that defines a portion received within the first
indentation of the first feed horn; and wherein the linear axis of
the array is substantially aligned with the major axis of the
reflector.
2. The antenna of claim 1, wherein the three closely spaced antenna
feed horns are disposed within a common housing.
3. The antenna of claim 2, wherein the common housing further
comprises a low noise block down converter.
4. The antenna of claim 2, wherein the common housing further
comprises a circular polarizer.
5. The antenna of claim 1, herein the first feed horn defines a
second indentation, further comprising a third feed horn having an
exterior contour that defines a portion received within the second
indentation of the first feed horn.
6. The antenna of claim 5, wherein the first feed horn comprises a
substantially cross shape.
7. The antenna of claim 6, wherein the second and third feed horns
each comprise a substantially square or rectangular shape.
8. The antenna of claim 6, wherein the second and third feed horns
each comprise a substantially round or oval shape.
9. The antenna of claim 6, wherein the second feed horn comprises a
substantially round or oval shape and the third feed horn comprises
a substantially square or rectangular shape.
10. The antenna of claim 1, wherein the first feed horn comprises a
substantially cross shape.
11. The antenna of claim 10, wherein the second feed horn comprises
a substantially square or rectangular shape.
12. The antenna of claim 10, wherein the second feed horn comprises
a substantially round or oval shape.
13. An antenna configured to simultaneously receive signals from
multiple satellites that are closely spaced from the perspective of
the antenna; comprising: a common housing containing at least three
closely spaced antenna feed horns arranged in a linear array along
a linear axis, a low noise block down converter, and a circular
polarizer; a substantially elliptical reflector defining a major
axis for feeding signals to the closely spaced antenna feed horns;
a first feed horn of the array having an exterior contour that
defines a first indentation; and a second feed of the array horn
having an exterior contour that defines a portion received within
the first indentation of the first feed horn; and wherein the
linear axis of the array is substantially aligned with the major
axis of the reflector.
14. The antenna of claim 13, wherein the first feed horn defines a
second indentation, further comprising a third feed horn having an
exterior contour that defines a portion received within the second
indentation of the first feed horn.
15. The antenna of claim 14, wherein the first feed horn comprises
a substantially cross shape.
16. An antenna configured to simultaneously receive signals from
multiple satellites that are closely spaced from the perspective of
the antenna, comprising: a common housing containing at least three
closely spaced antenna feed horns arranged in a substantially
linear array along a linear axis and a low noise block down
converter; a substantially elliptical reflector defining a major
axis for feeding signals to the closely spaced antenna feed horns;
a first feed horn of the array having an exterior contour that
defines first and second indentations; a second feed horn of the
array having an exterior contour that defines a portion received
within the first indentation of the first feed horn; and a third
feed horn of the array having an exterior contour that defines a
portion received within the second indentation of the first feed
horn; and wherein the linear axis of the array is substantially
aligned with the major axis of the reflector.
Description
TECHNICAL FIELD
The present invention is generally related to antenna systems
designed to receive broadcast signals with circular polarity and,
more particularly, is directed to digital video broadcast satellite
(DVBS) antenna systems.
SUMMARY OF THE INVENTION
An increasing number of applications are requiring systems that
employ a single antenna designed to receive from and/or transmit to
multiple sources simultaneously (multiple satellites in
particular). In cases where the satellites are very close this
creates a challenge for reflector antenna systems often resulting
in compromised performance and/or increased cost and complexity. On
a given reflector system a feed (horn or radiating element) is
needed for each satellite to be received from (or transmitted
to).
The difficulty arises because relatively small spacing between
satellites requires relatively small spacing between feeds. These
small feed spacing limits the size of the feed and other parameters
making it difficult to achieve good of even adequate antenna
performance and cost. Previously, considerable compromises were
made on single reflector antenna systems. FIG. 1 provides an
example of a single reflector with 3 closely spaced speeds for
simultaneous reception from 3 satellites.
A specific example of where this challenge arises are in systems
requiring simultaneous reception from a Ku BSS band satellite at
101.degree. as well as one or more Ku BSS band or Ka band
satellites are about 2 deg (or less) away from the Ku BSS
satellite. The Ka band and Ku BSS satellites have lower EIRP (power
density on the ground) and are much closer to potential
interference sources (generally around 2.degree.). With this in
mind the Ka band and/or Ku band BSS performance requirements are
usually the dominated factors in determining antenna size and
shape. Therefore little or no compromises are acceptable in the
design and fabrication of the Ka band or Ku band FSS feeds, so the
Ka band and Ku band BSS feed horns should not be made inordinately
small. On the other hand the Ku-DBS band horn can be made
relatively small because the dish size required for Ka or Ku BSS is
oversized for the DBS service (with it's higher EIRP).
Current Compromised Approaches:
Some systems using modestly sized feeds limit how close the feeds
can be placed such that the feeds are farther apart than the ideal
feed separation resulting in wider than ideal angular separation
between the antenna beams associated with each feed. This results
in an angular bore sight errors on one or more of the beams. FIG. 2
shows this error and resulting loss in power.
Currently some DBS feed approaches use small circular wave-guides
without employing dielectric material. Although fairly small there
are still inherent limits on how small these circular wave-guide
feeds can be made and correspondingly how close adjacent feeds can
be placed. This in turn can cause the bore-sight errors and
performance degradations discussed above. FIGS. 3a,b show a typical
situation where circular radiators are used next to elliptical or
rectangular feed(s). In this example very little space is available
between the feeds. They are probably to close for die-casting the
wall needed between them. Typically 0.05'' thickness is needed for
the wall.
Other systems introduce dielectric material into the DBS feed(s) in
order to reduce size. These dielectric feeds can generally be made
small enough to allow the feeds to be placed at the correct
location (separation) to eliminate bore sight errors but dielectric
material introduces loss sacrificing antenna gain and noise
temperature. Cost and manufacturing complexity is also generally
increased with the addition of a dielectric material. In addition
many implementations extend the dielectric material well beyond the
circular wave-guide in order to improve the feeds directivity and
match. The phase center of such a feed is usually somewhere between
the end of the dielectric and the metal wave-guide. This can pose a
problem to the adjacent feeds if a portion of the dielectric feed
partially blocks the path the adjacent feed(s). FIGS. 4a,b show how
dielectric shrinks the circular feed diameter providing more space
between the feeds. It also shows how the dielectric sticks out in
front of the feeds causing blockage of energy into the adjacent
feeds at some angles of incidence.
Increasing the focal length (or f/d=focal length to diameter ratio)
is another technique commonly used to increase the feed spacing
required for a given satellite spacing. However increasing the
focal length makes the feed support arm longer increasing cost
and/or degrading mechanical stability. In addition for longer focal
length antenna's feeds must be either larger (increasing cost) or
gain, noise temperature and pattern performance will degrade due to
excessive spill over (energy spillover the reflector due to
inadequately directive feeds).
Dual reflector systems can be used to increase feed spacing and
improve performance but these systems generally increase cost and
complexity. There is, therefore, a continuing need for a
multi-beam, multi-band antenna with closely spaced antenna feed
horns operable for simultaneously receiving signals from multiple
satellites that are closely spaced from the perspective of the
antenna.
SUMMARY OF THE INVENTION
The invention provides a solution to the problems discussed above
by using wave guide structures that are narrower than circular wave
guide structures particularly in the direction that allows
additional feeds to be placed very closely in order to reduce or
eliminate bore sight errors without the introduction of dielectric
material and without substantial increases in focal length. So this
invention immediately minimizes cost and improves performance by
eliminating dielectric losses and keeping the feed support arm
short. In addition this invention has several possible embodiments
most of which are easily manufactured in high volume because they
can be integrated directly into the LNBF die-cast housing.
Furthermore for circular polarity most of the embodiments of this
invention allow a CP polarizer to also be integrated directly into
the housing. This invention has obvious advantages on single
reflector systems but could also be used in dual reflector systems
where feed spacing is still a concern.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a is a top view of an antenna that includes three closely
antenna feed horns.
FIG. 1b is side view of the antenna of FIG. 1.
FIG. 2 is a graphical illustration of boresight error caused by
antenna feed offset in the antenna of FIG. 1.
FIG. 3a is a conceptual perspective side view of a three-horn
antenna feed block including a round feed horn located between an
elliptical feed horn and a rectangular feed horn.
FIG. 3b is a front view of the three-horn antenna feed block of
FIG. 3a.
FIG. 4a is a conceptual perspective side view of a three-horn
antenna feed block including a round feed horn with a dielectric
cone located between an elliptical feed horn and a rectangular feed
horn.
FIG. 4b is a front view of the three-horn antenna feed block of
FIG. 4a.
FIG. 5a-w excluding FIGS. 5l and 5o, consisting three drawing
sheets, shows conceptual front views of 21 possible antenna feed
horn aperture configurations.
FIG. 6a is a conceptual perspective side view of a three-horn
antenna feed block including a square feed horn located between an
elliptical feed horn and a rectangular feed horn.
FIG. 6b is a front view of the three-horn antenna feed block of
FIG. 6a.
FIG. 7a is a conceptual perspective side view of a three-horn
antenna feed block including a cross shaped feed horn located
between an elliptical feed horn and a rectangular feed horn.
FIG. 7b is a front view of the three-horn antenna feed block of
FIG. 7a.
FIG. 7c is a conceptual perspective side view of a three-horn
antenna feed block including a cross shaped feed horn located
between an elliptical feed horn and a square feed horn.
FIG. 7d is a front view of the three-horn antenna feed block of
FIG. 7c.
FIG. 8a is a perspective view of a small square horn with a
circular polarity polarizer that transitions from circular to
elliptical and back to circular waveguide.
FIG. 8b is a perspective view of a small square horn with a
circular polarity polarizer that transitions from square to
rectangular and back to square waveguide.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The embodiments of the present invention meet the challenge of
designing and manufacturing a single antenna with multiple closely
spaced feed horns for simultaneous reception from (and/or
transmission to) multiple satellites that are closely spaced from
the perspective of the antenna. The feed horns and associated
circular polarity antenna systems for multiple-beam, multi-band
antennas are designed to achieve good circular polarity performance
over broad and multiple frequency bands.
In general, elliptically and other shaped horn apertures are
described in the examples in this disclosure, however this
invention can be applied to any device that introduces phase
differentials between orthogonal linear components that needs to be
compensated for in order to achieve good CP conversion and cross
polarization (Cross polarization) isolation including but not
limited to any non-circular beam feed, rectangular feeds, oblong
feeds, contoured corrugated feeds, feed radomes, specific reflector
optics, reflector radomes, frequency selective surfaces etc.
To simplify the discussions, examples in this disclosure primarily
refer to reception or signals and generally referred to a single
circular polarity. However reciprocity applies to all of these
embodiments given they are generally low loss passive structures.
Furthermore the horns, CP polarizers and phase compensation
sections obviously support both senses of CP (RHCP and LHCP). If
both senses are impinging on the horn then they will be converted
to 2 orthogonal linear polarities that can be easily picked up with
2 orthogonal probes and/or slots etc. So the approaches described
in embodiments 1 and 2 can be used for systems transmitting and/or
receiving power in any combination of circular polarities: single
CP or Dual CP for each band implemented including multiple widely
spaced frequency bands.
It should be pointed out that for simplicity, specific phase values
were often given in the examples, but the phase compensation
concepts explained above are general. For example, the following
applies to embodiment #2: If the elliptical horn introduces X
degrees phase differential then the opposite slop phase
differential section should introduce 90-X degrees so that the
total introduced phase differential is 90 degrees=X -(90-X).
For simplicity the inventor provides examples using a nominal 90
degrees phase differential between orthogonal linear components as
the target for achieving CP conversion however it is understood
that a nominal -90 degrees or any odd integer multiple of -90 or 90
degrees will also achieve good CP ( . . . -630, -450, -270, -90,
90, 270, 450, 630 etc.) and this invention covers those cases as
well. As an example for embodiment 2 the horn could introduce a 470
degrees phase differential and the opposite phase slop section
could introduce a -200 degrees phase differential resulting in a
total 270 degrees phase differential.
In addition, a skilled antenna designer will understand that the
term "CP polarizer" is not limited to a device achieving a
theoretically perfect conversion from circular polarity to linear
polarity, but instead includes devices that achieves a conversion
from circular polarity to linear polarity within acceptable design
constraints for its intended application.
FIGS. 1a-b is a top view of an antenna 100 that includes three
closely antenna feed horns 104a-c.
FIG. 2 is a graphical illustration 200 of boresight error caused by
antenna feed offset in the antenna 100.
FIGS. 3a-b is how a three-horn antenna feed block 300 including a
round feed horn 302 located between an elliptical feed horn 304 and
a rectangular feed horn 306.
FIGS. 4a-b show a three-horn antenna feed block 400 including a
round feed horn 402 with a dielectric cone 404 located between an
elliptical feed horn 406 and a rectangular feed horn 408.
FIGS. 5a-w excluding FIGS. 5l and 5o, consisting three drawing
sheets, shows conceptual front views of 21 possible antenna feed
horn aperture configurations 501 through 521.
FIGS. 6a-b show a three-horn antenna feed block 600 including a
square feed horn 602 located between an elliptical feed horn 604
and a rectangular feed horn 606.
FIGS. 7a-b show a three-horn antenna feed block 700 including a
cross shaped feed horn 702 located between an elliptical feed horn
704 and a rectangular feed horn 706.
FIGS. 7c-d show a three-horn antenna feed block 740 including a
cross shaped feed horn 742 located between an elliptical feed horn
744 and a square or diamond feed horn 746. In this embodiment, the
square or diamond shaped feed horn 746 has been rotated so that a
corner of the feed horn fits into a corner of the cross shaped feed
horn 742 to further reduce the feed horn spacing in this
embodiment.
FIG. 8a shows a horn and polarizer assembly 800 including a small
square horn 806 with a circular polarity transition/polarizer
section 804 that transitions from circular to elliptical and back
to circular waveguide at the circular waveguide port 802.
FIG. 8b shows a horn and polarizer assembly 840 including a small
square horn 826 with a circular polarity transition/polarizer
section 824 that transitions from square to rectangular and back to
square waveguide at the square waveguide port 822.
BASIC DESCRIPTION/PRINCIPLES OF THIS INVENTION
As discussed above many other approaches use circular wave-guide
radiators when size and spacing is limited. However at a given
frequency the circular wave-guide can only be made so small before
it's dominate mode of propagation is severely attenuated.
The basic principle of this invention is the use of other
wave-guide geometries that can be made narrower than circular
radiators, particularly in the direction to allow adjacent feeds to
be placed closer together. The inventor recognized that a variety
of geometries can be used to accomplish this including simple
squares, cross or star structures, with sharp or generously
radiuses corners as depicted in FIGS. 5a-w excluding FIGS. 5l and
5o. As can be seen many of these structures are quite
simple/elegant and would be relatively easy to produce and
integrate into an LNBF casting. The shapes range from distinctively
cross-shaped geometries to nearly square, and some are even oblong.
All allow adjacent feeds to be put closer than a circular feed
would allow, because they can have a smaller width in that
direction without significantly attenuating the signal in
comparison to the traditional circular wave guide that has a
relative high cutoff frequency.
So in many cases these wave-guide structures will allow for
sufficiently small (narrow) feed sizes and close feed spacing,
however if needed dielectrics could be employed to further reduce
the width of the feed.
FIGS. 6a,b show an embodiment of this invention that uses a square
radiator. It could easily transition into a circular polarity
polarizer (for converting 2 CP signals into 2 linear modes) by
gradually changing from the symmetric wave guide structure (near
the square radiator) to a slightly asymmetric structure to
introduce the proper phase shifts of the 2 orthogonal linear
components (that make up a given circular polarity signal) and then
by finally transitioning to a circular wave guide convenient for
direct integration into an LNBF. In this example the square
radiator was conservatively chosen to be 0.532 inches across
corresponding to a cut off frequency of 11.1 GHz which is well
below the frequency band of operation (12.2-12.7 GHz). This
provides considerably more space between the feeds (or the feeds
could be placed closer together). A circular wave-guide of that
same diameter (0.532'') has a cut off frequency of 13.0 GHz and
would therefore not even operate in the desired band. A circular
wave-guide would have to be 0.623'' in diameter in order to have a
cut off frequency of 11.1 GHz. 0.623'' is 17% increase in width
over the square wave-guide, providing less space for the feeds as
show in FIGS. 3a,b.
FIGS. 7a,b,c,d show another embodiment that uses a cross radiator
oriented such that the larger adjacent feeds can be located even
closer. In this particular example the horizontal length between
extreme opposing corners is only 0.478'' for a cross radiator
designed for 12.2-12.7 GHz. In addition if the adjacent feeds are
elliptical or circular in shape they can be even closer because the
cross radiator is extremely narrow along the horizontal line that
the feed centers lie on. This is even more pronounced if the
adjacent feeds are diamond shaped as shown in FIGS. 7c,d.
In a particular embodiment, the first feed horn receives a beam in
the frequency band of 12.2-12.7 GHz (Ku BSS band) from a satellite
located at 101 degrees west longitude, the second feed horn
receives a beam in the frequency band of 18.3-18.8 and 19.7-20.2
GHz (Ka band) from a satellite located at 102.8 degrees west
longitude, and a third feed horn receives a beam in the frequency
band of 18.3-18.8 and 19.7-20.2 GHz (Ka band) from a satellite
located at 99.2 degrees west longitude.
Recall that a typical CP polarizer simply introduces a 90 deg phase
differential between the 2 orthogonal linear components that
comprise circular polarity. For all of the cross sections discussed
as possible embodiments a circular polarity "CP" polarizer can be
added and/or in some cases integrated to this small radiator
structure.
FIGS. 8a-b provide examples of this consisting of a small horn
section followed by a circular waveguide polarizer section in which
orthogonal sets of walls transition at different rates along the
length of the polarizer so that the height does not equal the width
of the waveguide cross-section over an appropriate length in order
to introduce the needed 90 deg phase differential is introduced. In
these examples relatively smooth transitions were used along the
length of the polarizer but abrupt steps can be used instead in
order to reduce length. Obviously traditional metal septums, irises
and dielectric polarizers can be used as well to introduce the
needed phase shift. Many approaches can be integrated (small
radiator and polarizer) into a single die-casting possibly
including the LNB (low noise block down converter) housing, or
simply connect to an OMT (orthogonal mode transducer). FIGS. 8a-b
also include a CP polarizer as part of the transition from small
radiator to output wave-guide. Near the middle of the
transition/polarizer, the x-section width is greater than the
height. This in combination with the correct length provides the
mechanism to introduce the 90 deg phase differential needed for
good CP conversion and cross polarization performance (x-pol
isolation).
* * * * *